Free cutting steels

ABSTRACT

This invention relates to free cutting steels containing in combination calcium and at least one free cutting element selected from the group consisting of lead, sulfur and tellurium. Such free cutting steels are characterized by their cutting property.

United States Patent [72] Inventors Tetsuro Ito Nagoya; Goshi Kato,Tsushima; Atsuyoshi Kimura, Chita-gun, all of Japan [2]] Appl. No.781,520

[22] Filed Dec. 5, 1968 [45] Patented Jan. 1 1, 1972 [73] Assignee DaidoSeiko Kabushiki Kaisha Minami-ku, Nagoya, Aichi, Japan [32] PriorityApr. 3, 1968 [3 3 Japan [54] FREE CUTTING STEELS 1 Claim, 24 DrawingFigs.

[52] US. Cl 75/125,

75/123 AA, 75/123 F, 75/126 C, 75/126 G, 75/126 M [51] Int. Cl

C22c 39/54 [50] Field ofSearch ..75/l23, 123 R, [23 AA, l23 F, 125,1266, 126M [5 6] References Cited UNITED STATES PATENTS PrimaryExaminer- L.-Dewayne Rutledge Assistant Examiner-Joseph E. LegruAttorney-Wenderoth, Lind & Ponack Gagnebin ABSTRACT: This inventionrelates to free cutting steels containing in combination calcium and atleast one free cutting element selected from the group consisting oflead, sulfur and tellurium. Such free cutting steels are characterizedby their cutting property.

PATENIEDJAIII 1 I972 3.634.074

SHEET um 12 FLANK WEAR WIDTH CUTTING TIME (M IN.)

CRITICAL REDUCTION IN HEIGHT ILI INVENTORS TETSURO ITO FIG. 2 GOSHI KATOATSUYOSHI KIMURA PATEF: 1511 1 :11 1 2912 E? Q 834 0174 RAKE FACE OFTOOLAFTER TI-IE RAKE FACE OF TOOL AFTER SSOCN STEEL WAS CUT THE S50 CYSTEEL WAS CUT RELIEF FACE OF TOOL AFTER RELIEF FACE OF TOOLAFTER THEQOCN STEEL WAS CUT TI-IE S5OCY STEEL WA CUT FIG.7

RAKE FACE OF TOOL AFTER RAKE FACE OF TOOL AFTER THE SSOCF STEELWAS CUTTHE SSOCYF STEELWAS CUT FIO.7

RELIEF FACE OF TOOL AFTER RELIEF FACE OF TOOL AFTER THE S5OCF STEEL WASCUT TI-IE S50 CYF STEELWAS CUT //vI/EN 70R$ TETSURO ITO. GOSHI KATO.

ATSUYOSH KIMURA' ZMJQ-m A TTORNEVS PATENTEU JAN] 1 1972 3334074 SHEETcan; 12

FIG. l5

. I I l 1 l l 1 1 1 1 I 20 40 a0|oo|so2oo3o04ooeoosoo9ooaoo20oo LIFE OFTOOL (MIN) FIG. l6

CUTTING SPEED INVENTOR5 TETSURO ITO 605 H I KATO ATSUYOSHI K IMU RAATTORNEYS FIG.

PATENTED JAN] 1 I872 SHEET 09 0F 12 6O .1 1 I. LMIMLWL. .1. J

20 40 so I00 I50 200 300 400 600 LIFE OF TOOL (MINJ FIG. 7

500 200 0 THE END OF TOOL ll K'Oll DISTANCE FROM THE END OF TOOL (JJ-ITHE END OF TOG.

L IIKIOU 500 400 300 200 I00 0 DISTANCE FROM THE END OF TOOL p)INVENTORS TETSURO no sosm KATO ATSUYOSHI K I MURA PATENTEI] m1 1 19723634074 SPEETv IUUF 12 l I 1 1 700 e00 500 400 300 200 I00 0 DISTANCEFROM THE END OF TOOL THE Tag TOOL FIG. I93 FE l I l l 700 600 500 400300 200 I00 0 DISTANCE FROM THE END OF TOOL 11-) THE END O TOOL "mo"FLANK WEAR WIDTH CUTTING TIME (MIN.)

FIG. 20

INVENTORS TETSURO ITO GOSH! KATO ATSUYOSHI KIMURA ATTORNEYS PAIENTED mu1 I372 ROCKWELL HARDNESS "c" SHEET 1 1 U? 1|||111||||||1411 2468IOl2l4l6l820222426'28303234xfi" NORMILIZED AT THE INDICATED DISTANCEFROM THE END OF STEELS (INCH) FIG. 2!

I '20 E oSCM3N 5 I00 SCM3Y g ASCM3F 8o ASCM3YF N 60 (I g FIG. 22

e5 4 24 60 E 03 22 55 5 v g 5 I8 45 F 5 [6 E 3 l4 l2 J [INN/mo so [)0 noI20 I30 TETSURO To TENSILE STRENGTH 9 Mme) GOSH! KATO ATSUYOSHI KIMURAjZ/M4m%;/MM i/m/Mz ATTORNEYS FREE CUTTING STEELS This invention relatesto free cutting steels containing in combination calcium and at leastone member selected from the group consisting of lead, sulfur andtellurium.

The cutting technique and workability of the steels are recognized to beof great importance in order to meet the increased production of thesteel articles and various kinds of free cutting steels have beendeveloped by incorporating one or more members, in combination, selectedfrom the group consisting of sulfur, lead, selenium, tellurium, bismuth,phosphorus and nitrogen with steels. Recently, free cutting steelscontaining calcium have come to draw the attention of those in the artdue to the facts that they produce a deposition layer on a cutting toolfor preventing the abrasion of tool and improve the life of tool.

The copending Japanese Pat. application No. 59,620 filed on Sept. 19,1967 discloses the free cutting steels containing anorthite as theprincipal oxide inclusion. Such free cutting steels contain calcium inan amount varying from p.p.m. to 100 p.p.m. (0.002 to 0.01 percent byweight).

Also the copending Japanese Pat. application No. 14,630 filed on Mar. 3,1968 discloses the free cutting stainless steels containing calcium inan amount varying from 100 p.p.m. to 600 p.p.m. (0.01 to 0.06 percent byweight). The base steels contain Cr or Cr and Ni or Cr and Mn or Cr, Niand Mn as the principal alloying elements.

The inventors have found that such a Ca-containing free cutting steelimproves the life of tool when it is cut under high speed but it doesnot improve the life of tool when it is out under low speed as comparedwith the life of tool when the base steel not containing the freecutting additive or additives is out under low speed. In thisconnection, it was reported and recognized in the art that the freecutting steels containing the single member or in combination, moremembers selected from the group consisting of Pb, S and Te remarkablyimprove the life of tool when they are cut under low or medium speed butthat they slightly improve the life of tool when they are cut under highspeed.

The object of this invention is to provide free cutting steels withoutthe above-mentioned defects as inherent to the conventional free cuttingsteels. The object of this invention can be achieved by providing thefree cutting steels containing in combination calcium and at least onemember selected from the group consisting of Pb, S and Te.

The inventors have found that the free cutting steels in accordance withthis invention are remarkably improved in their mechanical properties,workability and etc., as compared with the free cutting steelscontaining Ca or Pb or Pb, S and Te when they are cut under low ormedium or high speed, and also that the free cutting steels inaccordance with this invention have the abrasion resistance,hardenability, cold and hot workability similar to those of the basesteels. It should be noted that the base steels used in this inventionhave the following chemical compositions.

in accordance with this invention, the base steels must contain as thefree cutting elements calcium in an amount of from 0 0.0010 to 0.030percent by weight and at least one member selected from lead in anamount of from 0.03 to 0.35 percent by weight, sulfur in an amount ofbelow 0.5 percent by weight and tellurium in an amount of from 0.01 to0.10 percent by weight for producing the subject free cutting steelshaving the improved cutting property and workability. The inventors havefound that the free cutting steels are not improved in their workabilitywhen they contain calcium in an amount outside the range as definedabove. Also, the inventors have found that the free cutting steels aredecreased or not imiproved in their workability when they contain Pb, Sand Te in an amount outside the range as defined above.

Further there are explained hereinafter the reasons why the amount ofthe components contained in the base steels is defined within the rangeas mentioned above.

The lower limit of carbon is defined to 0.05 percent by weight forobtaining the necessary strength for the steels. The upper limit ofcarbon, silicon or manganese is defined to 0.30, 2.0 or 4.0 percent byweight for obtaining the necessary tenacity and workability for thesteels. Phosphorus is an additive for increasing the workability of thesteels but the amount of phosphorus is defined to the upper limit of a1.0 percent by weight because the tenacity and ductility of the steelsare affected as the phosphorus content increases. The upper limit ofnickel, chromium or molybdenum is defined to 5.0, 6.0 or 1.0

percent by weight because the workability of the steels are decreasedwhen the steels contain Ni, Cr or M0 in a larger amount over the upperlimit thereof. Tungsten is harmful to workability; copper causesbrittleness; titanium, vanadium and niobium are harmful tohardenability; and foron is harmful to workability of the steels as thecontent thereof increases and thus their upper limit is defined to 1.0,0.5, 0.5, 0.5 and 0.01 percent by weight respectively.

Examples of the free cutting steels in accordance with this invention aswell as the base steels and control steels are listed in the followingtable 1 TABLE 1 Chemical components Hardgrmss Steels C Si Mn P S Cu CrMo Pb Te Ga normalized ZO N base 0.21 0.24 0.38 0.018 0.012 .13 0.08 15120UF 0.20 0.31 0.40 0.018 0.015 3.12 0.11 160 S20CY 0.21 0.31 0.50 0.0210.016 0.12 0.10 153 S20CY 0.20 0.28 0.88 0.019 0.016 0.12 0.10 151 SEOCN(b 0.51 0.28 0.75 0.014 0.018 0.11 0.10 215 S5001 0.50 0.29 0.78 0.0160.019 0.16 0.14 213 S500 0.51 0.30 0.74 0.014 0.020 0.10 0.13 215 S50CYF0.50 "0,27 0.68 0.016 -0.020 0.16 0.12 214 SFCBF..- 0.08 0.10 0.99 0.0680.318 0.12 0.16 124 SFC3YF- 0.00 0.09 1.01 0.071 0.321 0.11 0.16 123SFC3FT 0.07 0105 0.99 0.075 0.321 0.13 0.16 126 SFO3FTY 0.08 0.06 0.980.075 0.316 0.13 0.15 124 SUM1B(b8S9) 0.11 0.18 0.78 0.014 0.183 0.230.10 lBY 0.10 0.20 0.76 0.015 0.181 0.20 0.11 122 SCM3N (bBSe) 0.35 0.290.69 0.018 0.012 0.14 1.00 269 CM3Y 0.36 0.28 0.69 0.016 0.013 0.12 0.98269 SCMBF.-- 0.35 0.31 0.71 0.017 0.013 0.12 0.98 270 a F 0.35 0.30 0.700.018 0.011 0.12 1.00 270 In table I, it is noted that the base steelsare S20CN, S50CN, SUMIB and SCM3N as designated in the JapaneseIndustrial Standards, and F-type, Y-type and YF-type steels containlead, calcium and lead plus calcium respectively.

Now, this invention is fully explained by referring to the accompanyingdrawings in which:

FIG. 1 shows curves illustrating the relationship between the flank wearwidth and the cutting period of time when SZOCN, SZOCF, S20CY and SZOCYFsteels were normalized and then cut at the feed of 0.2 mm./rev., thedepth of cut of 2.0 mm. and the cutting speed of 200 m./min. by usingthe cutting tool P 10 having the back rake angle of -5, the side rakeangle of 5, the end relief angle of 5, the side relief angle of 5, thecutting angle of 30, the side cutting angle of and the l nose radium of0.4 mm. It can be seen from the curves as indicated in FIG. 1 that theS20CYF steel of this invention which contains 0.18 percent of Pb and0.0051 percent of Ca is remarkably improved as compared with the S20CFsteel and the SZOCY steel. When the steels were cut for 60 minutes, theflank wear width of the tool is given in the following table 2.

The above-mentioned steels were normalized to have the hardness (I-IB)of 135 and test pieces were madeof the normalized steels. The testpieces have the size of 6 mm.Xl2 mm. and they were tested for thecritical reduction in height. The test was condueed for 20 times in eachof the steels. The results of the test are shown in FIG. 2. As it isobvious from FIG. 2, the S20CYF steel of this invention has the coldworkability similar to that of the S2OCN steel but higher coldworkability than that of the S20CF steel containing Pb alone. It shouldbe understood that the critical reduction in height (11L) is indicatedby the following equation.

wherein, H indicates the initial height of the test piece and hindicates the final height of the test piece after it was compressed.

Also the above-mentioned steels were tested for hot workability. Thetest pieces having the size of 8 mm. 30 mm. were made of the steels andthe test pieces were tested for the torsion value for initiating thebreaking of them at the strain speed of 2 sec. at l,l00 C. by using thehigh temperaturetorsion test machine. The results of the tests are shownin FIG. 3. As it is obvious from FIG. 3', the SZOCYF steel of thisinvention has the hot workability similar to that of the S20CN steel buthigher hot workability than that of the S20CF steel containing Pb alone.

Free cutting steels were produced by incorporating various amounts ofcalcium and lead with SSOCN steel and then they were normalized. Thenormalized free cutting steels were cut at the feed of 0.20 mm./rev. andthe depth of cut of 2.0 mm. under high cutting speed by using a cuttingoil and the cutting tool P 10" having the back rake angle of 5, the siderake angle of 5, the end relief angle of 5, the side relief angle of 5,the end cutting angle of 30, the side cutting angle of 0 and the noseradium of 0.4 mm. The life of tool was evaluated at the flank wear widthof 0.3 mm. The results of the tests are shown in FIG. 4. In FIG. 4, thelife of tool is indicated by using the abbreviation (T) of the multiplenumber calculated by assuming that the life of tool is 1.0 when theSSOCN steel was cut. As it is obvious from FIG. 4, the life of tool isremarkably improved as the amount of Ca and Pb contained in the freecutting steels increase and also the life of tool is improved byincreasing the amount of Ca even if the amount of Pb is decreased.

FIG. 5 shows the life of tool when the SZOCN, SSOCY. SCF and SSOCYFsteels were normalized and cut under low speed. The normalized basesteel and the free cutting steels were cut at the feed of 0.12 mm./rev.and the depth of cut of 1.0 mm. under high cutting speed of 50 m./min.by using a cutting oil and the cutting tool SKH4" having the back rakeangle of 0, the side rake angle of 15, the end relief angle of 7, theside relief angle of 7, the end cutting angle of 10, the side cuttingangle of 0 and the nose radius of 0.5 mm. The life of tool was evaluateduntil the tool becomes to have no ability for cutting the test samples.As it is obvious from FIG. 5, the free cutting steel designated as SSOCYsteel, which contains calcium alone, is not improved in its workabilityas compared with the base steel designated as SSOCN steel butthe freecutting steel designated as SCSOCYF, which contains calcium and lead incombination, is remarkably improved in its workability as compared withthe base steel.

FIG. 6 shows curves illustrating the relationship between the cuttingspeed and the roughness of the finished surface of each of SSOCN, SSOCY,SSOCF and SSOCYF steels when they were normalized and cut. The testswere conducted by cutting the normalized steels at the feed of 0.25mm./rev. or 0.35 mm./rev. and the depth of cut of 2.0 mm. under theindicated cutting speed by using the cutting tool P 10" having the backrake angle of 5, the side rake angle of 5 the end relief angle of 5, theside relief angle of 5, the end cutting angle of 30, the side cuttingangle of 0 and the nose radius of 4 mm. As it is obvious from FIG. 6,the free cutting steel (SSOCYF steel) of this invention indicates to tohave the good finished surface.

Also, the normalized steels as mentioned above were cut at the feed of0.18 to 0.48 mm./rev. and the depth of cut of L0 mm. by using thecutting tool P 10" having the back rake angle of 0, the side rake angleof 6, the end relief angle of 7, the side relief angle of 7, the endcutting angle of 10, the side cutting angle of 0 and the nose radius of0.5 mm. The cut scrap was crushed for testing its brittleness by using achip breaker and it is found that the cut scrap obtained by cutting theSSOCYF steel of this invention can easily be crushed without the use ofthe chip breaker. The results of tests are given in the following table3.

TABLE 3 SSOCN SBOCY S50CF SHJCYF PPPPPPPPPPPPPPPPPPPPsaeessesseaseseessee mqoexxooooxoooxw kww NN NMO O NM NNN NNNoooooooooooooooo o ooooooooooooooooxgm Note: The mark X indicates theuse of the chip breaker for crushing the cut scrap and the mark 0indicates that the chip breaker is not required for crushing the cutscrap.

FIG. 7 shows the microphotographs illustrating the fatigue state of therake face and the relief face of the tool when S50CN, SSOCY, SSOCF andSSOCYF steels were cut with the cutting tool. As you see from thernicrophctographs, it is observed that the rake face and the relief faceof the tool were abraded when the SSOCN steel was cut. Also, it isobserved that the abrasion of the rake face and the relief face of thetool was considerably prevented due to the presence of the layerdeposited on the rake and relief faces when the S50CY and S50CF steelswere cut. Further, it is observed that the tool was not obraded when theSSOCYF steel was cut.

FIG. 8 shows curves illustrating the relationship between tensilestrength and proof stress or elongation or a 0.2 percent reduction ofarea when SSOCN, SSOCYN, SSOCNF and SSOCYF steels were tested. As yousee from the curves, the steels have the similar mechanical propertiesin the proof stress, elongation and the reduction of area and thereforeit is understood that the mechanical properties of the SSOCYF steel arenot affected by the presence of calcium and lead.

FIG. 9 shows a curve illustrating the relationship between Charpy impactstrength and hardness of SSOCN, SSOCY, S50CF and S50CYF steels when theywere heated at 800 C. and annealed at 550 600 or 650 C. As you see fromthe curve, the mechanical properties of the SSOCYF steel are notaffected by the presence of calcium and lead.

FIG. 10 shows curves illustrating the change of fatigue strengthaffected by the presence of calcium and lead contained in S50CN steel.The test was conducted for three times in each of the test steels andtheir fatigue strength are given as the average value. In FIG. 10, it isnoted that the fatigue strength is indicated by the multiple numbercalculated by assuming that the SSOCN steel has the fatigue strength of1.0.

The following table 4 shows the relationship between the life of thecutting tool and the fatigue strength of the three types free cuttingsteels designated as S50CY, SSOCF and SSOCYF steels. In table 4, it isnoted that the life of tool and the fatigue strength of steels areindicated by the multiple number using the abbreviation (T). Also it isnoted that SSOCY-l steel, S50C2 steel or S50CY3 steel contains 0.002%Ca, 0.005% Ca or from 0.007 to 0.016% Ca, S50CF-1 steel or S50CF-2 steelcontains 0.15% Pb or 0.20% Pb, and SSOCF-l steel, S50CYF-2 steel,SSOCYF-3 steel or SSOCYF-4 ste el contain 0.001% Ca plus 0.05% Pb,0.001% Ca plus 0.10% Pb, 0.002% Ca plus 0.05% Pb or 0.004% Ca plus 0.05%Pb.

It is understood from the data as shown in table 4 that the SSOCYF-typesteels have the fatigue strength similar to or above the fatiguestrength of the S50CY-type steels and also that the SSOCYF-type -typesteels have the larger fatigue strength than that of the SSOCF-typesteels.

Also, the following table 5 shows the relationship between the life ofthe cutting tool and the fatigue strength of the three types freecutting steels designated as S50CY, SSOCF and S50CYF steels. As in table4, the life of tool and the fatigue strength are indicated by using themultiple number. Further, it is noted that S5OCY4 or SSOCY-S steelcontains 0.010% Ca or 0.016% Ca; S50CF-2 or S50CF-3 steel contains 0.20%Pb or 0.25% Pb; and SSOCYF-S or S50CYF-6 steel contains 0.005% Ca plus0.05% Pb or 0.006% Ca plus 0.10% Pb.

19 hav the ha n TABLE 5 Fatigue strength Steels Life of tool S50CY-4 5 T0.94 T S50CF-2 4 T SSOCYF-S S T S50CY-5 5 T 0.89 T SSOCF-3 4 T SSOCYF-616 T As you see from the data as shown in table 5, the fatigue strengthof the SSOCYF-type steels is not so much decreased in spite of the highincrease of the life of the cutting tool.

FIG. 11 shows the cold workability of each of the steels designated asSSOCN, S50CY, SSOCF and SSOCYF. The steels were normalized to have thehardness (HB) of 135 and 20 test pieces were made of the normalizedsteels. The test pieces have the size of 6 mm. 12 mm. and they weretested for the critical reduction in height (L). As it is obvious fromFIG. 11, the S50CYF steel of this invention indicates substantially thesame critical reduction in height as that of the base SSOCN steel andeliminates the defect of the SSOCF steel containing Pb alone as the freecutting element.

FIG. 12 shows the hot workability of each of the steels as mentioned inFIG. 11. The test pieces have the size of 8 mm. 30 mm. and they weretested for the torsion value for initiating the breaking of them at thestrain speed of 5 sec. at 1,100 C. by using the high temperature-torsiontest machine. As it is obvious from FIG. 12, the S50CYF steel of thisinvention indicates the torsion value for initiating the breaking of itssimilar to that of the base SSOCN steel and eliminates the defect of theSSOCF steel containing Pb alone as the free cutting element.

FIG. 13 shows the abrasion resistance of each of the steels as mentionedin FIGS. 11 and 12. The steels were normalized s, HRClQ ?F t e srt wf-75 "I t-an test pieces were made of the normalized steels. The testpieces have the size of 30 mm. in the outside diameter and the contactsurface of 5 mm. in width. They were tested for their abrasionresistance. The test was conducted at 1,000 r.p.m. under the surfacepressure of 200 kg./mm. by using the abrasion test machine and thenumber of abrasion cycle for growing the pit was recorded. The resultsof tests are shown in FIG. 13. As it is obvious from FIG. 13, the SSOCYFsteel of this invention indicates substantially the same abrasionresistance as that of the base SSOCN steel.

Further, the steels as mentioned in FIGS. ll, 12 and 13 were tested fortheir crack at surface or root or in depth and it was found that theSSOCYF steel of this invention indicates good resistance against such asurface or root or depth crack as compared with that of the base SSOCNsteel and the such crack resistance of the SSOCYF is measured as in themiddle value of the S50CY steel containing Ca alone and the SSOCF steelcontaining Pb alone as the free cutting elements.

FIG. 14 shows curves illustrating the relationship between the life oftool and the cutting speed when the free cutting steels designated asSFC3F steel containing S and Pb, and SFC3FY steel containing S, Pb andCa were cut. The steels were normalized and the normalized steels werecut at the feed of0.l mm./rev. and the depth ofcut of0.5 mm. under theindicated cutting speed by using the cutting tool K 10' having the backrake angle of 0, the side rake angle of 6, the end relief angle of 7,the side relief angle of 7, the end cutting angle of 10, the sidecutting angle of 0 and the nose radius of 0.5 mm. The life of tool wasevaluated at the flank wear width of 0.2 mm. As it is obvious from thecurves shown in FIG. 14, the SFC3F Y steel of this invention gives alonger life of tool as compared with the SFC3F steel.

FIG. 15 shows the hot workability of the steels as shown in FIG. 14. Thetest pieces have the size of 8 mm.X30 mm. and

they were tested for the torsion value for initiating the breaking ofthem at the strain speed of 3 sec. at l,l50 C. by using the hightemperature-torsion test machine. As it is obvious from FIG. 15, theSFC3FY steel is improved in the torsion value as compared with the baseSFC3F steel.

FIG. 16 shows curves illustrating the relationship between the life oftool and the cutting speed when the free cutting steels designated asSFC3FT steel and SFC3FI Y steel were cut. It is noted that the SFC3FTsteel contains sulfur, lead and teliurium, and the SFC3FT Y steelcontains sulfur, lead, tellurium and calcium as the free cuttingelements. The steels were normalized and the normalized steels were cutat the feed of 0.1 mm./rev. and the depth of cut of 0.5 mm. under theindicated cutting speed by using the cutting tool K having the back rakeangle of 0, the side rake angle of 6, the end relief angle of 7, theside relief angle of 7, the end cutting angle of 10, the side cuttingangle of0 and the nose radius of 0.5 mm. The life of tool was evaluatedat the flank wear width of 0.2 mm. As it is obvious from the curvesshown in FIG. 16, the SFC3FT Y of this invention gives a longer life oftool as compared with the base SFC3F'I steel.

FIG. '17 shows curves illustrating the relationship between the life oftool and the cutting speed when the free cutting steels designated asSUMIB steel and SUMIBY steel were cut. It is noted that the SUMIB steelcontains sulfur and the SU- M IBY steel contains sulfur and calcium asthe free cutting elements. The steels were normalized and the normalizedsteels were cut in the same manner as in the tests conducted andexplained in FIG. 16. The life of tool was evaluated at the flank wearwidth of 0.2 mm. As it is obvious from the curves shown in FIG. 17, theSUMIBY steel of this invention gives a longer life of tool as comparedwith the base SUMIB steel.

FIGS. 18 and 19 show distribution of the characteristic X- ray emissiondensity emitted from sulfur and iron contained in the deposited layer onthe rake face of tool after the tool was used for cutting the steelsdesignated as SUMIB steel and SU- MIBY steel. Both the steels were cutat the feed of 0.1 mm./rev., at the depth of cut of 0.5 mm. and at thecutting speed of 180 meters per minute for 20 minutes by using a cuttingoil and the cutting tool K 10" as explained in the above mentionedtests. FIG. 18 shows the results of test when the tool is used forcutting the SUMIB steel and a considerable amount of Fe is observed overthe range varying from the end of the tool to about 250;4.. This provesthat the rake face of the tool was directly contacted with the scraps ofthe steel. FIG. 19 shows the results of test when the tool is used forcutting the SUMIBY steel and a considerable amount ofS (or CaS) isobserved all over the tool but Fe is not observed over the range varyingfrom the end of the tool to about 5011.. This proves that the rake faceof the tool was coated with the thin layer containing sulfur and thetool was prevented from abrasion.

FIG. 20 shows curves illustrating the relationship between the flankwear width and the cutting speed when Cr-Mo alloy steel designated asSCM3N and free cutting steels designated as SCMBY, SCM3F and SCM3YFsteels were cut with tool. It is noted that the SCM3Y steel containscalcium, the SCM3F steel contains lead and the SCM3YF steel containscalcium and lead as the free cutting elements. As it is obvious from thecurves shown in FIG. 20, the SCM3YF steel of this invention is lessabrasion than the other steels. Also, it is noted that all the steelswere normalized and the normalized steels were cut at the feed of 0.2mm./rev. and the depth of cut of 2.0 mm. under the cutting speed of 200meters per minute by using the cutting tool P 10'' as mentioned in FIG.6.

Also the steels were tested for time in minutes until the flank wearwidth of the tool reached 0.30 mm. when the steels were cut with thecutting tool P 10 the results of tests are given in the following table6.

FIG. 21 shows curves illustrating the hardenability of the steels asshown in FIG. 20. As it is obvious from the curves as shown in FIG. 21,the SCM3YF steel of this invention has better hardenability than that ofthe SCM3N steel.

FIG. 22 shows curves illustrating the relationship between tensilestrength and elongation (percent) or 0.2 percent yield strength orreduction of area when the steels designated as SCM3N, SCM3Y, SCM3F andSCM3YF were tested. In FIG. 22, it should be noted that the SCM3N steelis indicated by the marks 0" and the SCMBY steel is indicated by themarks Also, the SCM3F steel is indicated by the marks A and t e SCM3YFsteel is indicated by the marks A As it is obvious from the curves asshown in FIG. 22, the SCM3YF steel of this invention has the mechanicalproperties similar to those of the other steels.

FIG. 23 shows a curve illustrating the relationship between hardness(HB) and Charpy impact strength when the steels designated as SCM3N,SCM3Y, SCM3F and SCM3YF were tested. It is noted that all the steels areindicated in the same marks as in FIG. 22 respectively. The steels werenormalized at 860 C. and then annealed at 500, 550, 600 and 650 C. As itis obvious from the curves as shown in FIG. 23, the SCM3YF steel of thisinvention has the Charpy impact strength similar to those of the othersteels.

FIG. 24 shows the cold workability of the steels designated as SCM3N,SCM3Y, SCM3F and SCM3FY when they were tested for critical reduction inheight (L). All the steels were normalized to have the hardness (HB) ofI and test pieces were made of the normalized steels. The test pieceshave the size of 6mm.Xl2mm. As it is obvious from FIG. 24, the SCM3YFsteel of this invention indicates substantially the same criticalreduction in height as that of the SCM3N steel and also indicates bettercritical reduction in height than that of the SCM3F steel containing Pbalone.

As stated in the foregoing, this invention provides the calciumcomposite free cutting steels which are manufactured by incorporatingcalcium and at least one member selected from the group consisting ofPb, S and Te with the carbon steels or the alloy steels. Such compositefree cutting steels are improved in their cutting property as comparedwith the free cutting steels which are manufactured by incorporatingcalcium alone or at least one member selected from the group consistingof Pb, S and Te with the carbon steels or alloy steels. In addition suchcomposite free cutting steels have the mechanical properties, cold andhot workability, hardenability, abrasion resistance and weldabilitysimilar to those of the original carbon steels or the original alloysteels.

What we claim is:

1. Free cutting carbon steel and alloy steel having improved cuttingproperties such that it may be cut at low or high speeds with animproved life to the cutting too], said steel being characterized bycontaining as the free cutting elements calcium in an amount of from0.0010 to 0.020 percent by weight and lead in an amount of from 0.03 to0.35 percent by weight.

zgz g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,634 O74 Dated January 11 1972 lnventofls) Tetsuro ITO, Goshi KA'IO andAtsuyoshi KIMURA It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2 line 37:

change "0.30" to Signed and sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLF,TCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

